single products ordered, Database Management System

For Colorado customers calculate the number of single products ordered. If a product is purchased on multiple orders, it should be counted only single time. The result should contain customer number, customer last name and the number of single products ordered.

Query:select c.CUSTNO,c.CUSTFIRSTNAME,c.CUSTLASTNAME,count(ol.ORDNO) from customer c,ordertblot,ordlineol,product p where c.custno=ot.custno and ot.ordno=ol.ordno and p.PRODNO=ol.PRODNO group by c.CUSTNO,c.CUSTFIRSTNAME,c.CUSTLASTNAME,ol.ordno;